A structural member including a tubular portion composed of a hat member with a hat-shaped cross section and a closing plate joined to the hat member is used for various applications. Applications include, for example, the use of a structural member in a vehicle, a building, and a large container. Especially structural members used in automobiles are required to have impact resistance.
For example, WO 2005/058624 (Patent Document 1) discloses a metal pipe mounted on the vehicle body of an automobile with its both ends supported thereon to provide impact resistance. This metal pipe includes a bent portion along its entire length or along a partial length. The pipe is disposed in such a manner that the outer side of the bent portion receives an impact expected to be applied to the vehicle body, where the outer side is generally aligned with the impact. This metal pipe has a better impact resistance than a reinforcing member using a straight pipe to reinforce the vehicle body.